A traction elevator car is supported by a wire rope which is attached at a first end to an elevator car and at a second end to a counterweight. The rope passes over a sheave which is driven by an electric motor. The motor raises or lowers the elevator car by traction forces generated between the wire rope and the sheave.
Usually, the drive sheave and electric motor are arranged above the elevator car in a machine room. In buildings, where space is at a premium, machine rooms are not desirable.
Hydraulic elevators are driven by a piston. The piston is usually disposed within a pit beneath the car, thereby obviating the need for a machine room. Building the pit and maintaining the piston therein is relatively time consuming and expensive, however. Hydraulic elevators have other drawbacks relative to traction elevators: the rise of the car is limited by the length of the piston; the speed of travel is inferior; and the weight of the car is not offset by a counterweight and therefore, hydraulic elevators utilize far more energy.
In U.S. Pat. No. 4,402,386 to Ficheux et al entitled "SELF-POWERED ELEVATOR USING A LINEAR ELECTRIC MOTOR AS COUNTERWEIGHT" and owned by the assignee herein, an elevator is shown that is driven by linear motor comprised of a tubular primary element disposed around a tubular secondary element. The linear motor does not require a machine room, as required by a traction elevator, and has no pit, as required by an hydraulic elevator. The linear motor is also energy efficient and fast relative to an hydraulic elevator. However, it has been found, to date, that it is impractical to hang a tubular secondary element over a given number of stories, thereby limiting the rise of the elevator.